The present invention relates to a method for controlling a corona ignition device.
Corona ignition devices generate a corona discharge during operation, with which fuel in the combustion chamber of an engine is ignited. Corona ignition devices are thus an alternative to conventional spark plugs, which ignite fuel by means of an arc discharge.
Corona ignition devices allow a much greater ignition volume in comparison with conventional spark plugs, which in an internal combustion engine results in a much better tolerance to lean burn and better combustion statistics. Corona ignition devices therefore have the potential to allow much more efficient engine operation. Corona ignition devices not only have efficiency and fuel consumption advantages over spark plugs but also can ignite more lean mixtures and therefore significantly reduce nitrogen oxide emissions.
A corona ignition device is described, for example, in U.S. Pat. No. 8,640,665. This corona ignition device has an ignition electrode, which is accommodated in an insulator and, together with a housing radially surrounding the insulator, forms a capacitor that is part of an oscillator circuit. Said oscillator circuit is excited to resonance with a high-frequency alternating voltage of, for example, 30 kHz to 50 MHz or more. A corona discharge can be generated at the ignition electrode in this manner. The high-frequency alternating voltage is generated from a primary voltage with a voltage converter.
The corona discharge at the ignition electrode of a corona ignition device becomes greater with greater applied voltage, i.e., greater high-frequency alternating voltage and primary voltage. However, an excessive voltage must not be applied to the corona ignition device, since the corona discharge becomes an arc discharge at a critical breakdown voltage. In known methods for controlling corona ignition devices, attempts are therefore made to select a voltage that is always as close to the breakdown voltage as possible, so that the greatest possible corona discharge can be formed while a transition of the corona discharge into an arc discharge can be reliably avoided.